Fixing devices incorporated in an electrophotographic image forming apparatus, such as copiers, facsimile machines, or printers, include a fixing device for fixing a toner image on sheet paper by heat pressing in which the sheet paper passes through the nip formed between a pair of rollers comprised of a heating roller and a pressing roller, or between a pair of belts. The surfaces of the heat fixing members such as the heating rollers or the heating belts are generally coated with a fluorocarbon-resin topcoat layer to obtain ability of release. Between the core rod and the topcoat layer has been provided a primer layer to increase in adhesion strength.
However, such heat fixing members have not given consideration to increasing the life of the fluorocarbon-resin topcoat layer. Accordingly, the topcoat layers have been worn down at a contact position with a cleaning unit, a thermo sensor, or a separation finger, resulting in a decrease in their life.
There is also an apparatus that heats a heat fixing member by an induction heating method. The induction heating method is a method in which a specified power is supplied to an induction heating coil to generate a magnetic field, and the conductive heat-generation layer of a heat fixing member is heated in a moment by an eddy current generated by the magnetic field, thereby allowing the heating roller or the heating belt to fix the toner image. As the heat-generation layer of the heat fixing member of such an induction heating method, iron-based materials have principally been used in recent years.
The adhesion between the heat-generation layer and the primer layer may be decreased depending on the material of the heat-generation layer of the heat fixing member. Accordingly, when the amount of the binder in the primer layer is increased to improve the adhesion with the heat-generation layer, the bonding force between the primer layer having much binder and the topcoat layer is decreased. On the other hand, with a fixing device of a high-speed machine in which the peripheral velocity of the heat fixing member is fast, to which a high linear load is applied by a press roller, significant mechanical and thermal stress is applied to the boundary between the primer layer and the topcoat layer of the heat fixing member. This might cause separation between the primer layer and the topcoat layer of the heat fixing member, thus decreasing the life of the heat fixing member.
This leads to the demand for a heat fixing member and a fixing device of an image forming apparatus in which the topcoat layer hardly comes off irrespective of the material of the heat-generation layer, and in which the abrasion of the topcoat layer can be prevented to increase the life even in a high-speed fixing device.